diff --git a/sklearn/inspection/partial_dependence.py b/sklearn/inspection/partial_dependence.py
index 47eb6c2d2..0e3dc2ad5 100644
--- a/sklearn/inspection/partial_dependence.py
+++ b/sklearn/inspection/partial_dependence.py
@@ -286,7 +286,7 @@ def partial_dependence(estimator, X, features, response_method='auto',
         raise ValueError(
             "'estimator' must be a fitted regressor or classifier.")
 
-    if (hasattr(estimator, 'classes_') and
+    if (hasattr(estimator, 'classes_') and estimator.classes_ is not None and
             isinstance(estimator.classes_[0], np.ndarray)):
         raise ValueError('Multiclass-multioutput estimators are not supported')
 
